One of the most important infant developmental accomplishments is fitting into the family life pattern, which is driven by circadian and diurnal (day-night) rhythms. Mothers serve an essential role in entraining infant circadian rhythm, synchronizing the immature infant circadian rhythm with the 24-hour day. The application extends current research supported by a career development award. The purpose of the proposed methodological study is to test infant and maternal actigraphy and infant urinary 6-sulfatoxymelatonin (6-sMT) as markers of circadian rhythm. Aims include determining the sensitivity threshold setting for computer scored actigraphy in infants, developing methods and protocols for performing actigraphy in mothers and infants collecting infant urinary 6-sulfatoxymelatonin in the home environment, testing the laboratory assay of infant urinary 6-sulfatoxymelatonin collected from diapers, and estimating the number of continuous days of actigraphy recording required to accurately portray circadian rhythm of mother and infant rest-activity pattern. The study will be conducted in two phases, each employing an intensive within subject design and including healthy term gestation infants and their mothers. In Phase 1, laboratory-based actigraphy will be conducted in ten mother-infant pairs over a two-hour period in conjunction with live observation and videotaping. Correspondence between live observation of activity and computer scored actigraphy will be assessed over a range of activity thresholds to define appropriate software sensitivity setting for the study of infants. In Phase 2, maternal-infant actigraphy will be conducted over a four-day period in the home. Infant diapers will also be collected over a 24-hour period. Urine samples will be extracted and urinary 6-sMT assayed. Prior to the home study, the diaper extraction procedures and ELISA assay will be tested by (1) instilling known concentrations of assay standard in diapers, extracting samples, and evaluating results against the assay standard curve, (2) examining differences between 6-sMT values from urine tested with and without diaper extraction. Circadian rhythm parameters (mesor, amplitude, acrophase based on cosinor analysis) will be calculated using one through four days of data to ascertain a data collection period that accurately portrays infant and maternal rest-activity pattern. Throughout both Phases mother's acceptability of study procedures will be assessed. Methods, refined in the low risk population, will subsequently be employed in the study of maternal entrainment of preterm infants.